A conventional power wrench, such as e.g. a nutrunner, comprises a transmission for providing a torque from a motor to a main shaft.
Normally, the motor is arranged to drive the rotation of the main shaft in two opposed directions, a first forward direction and a second reversed direction. Hence, the transmission needs to be adapted to drive the rotation both in the forward direction and the reversed direction.
In many applications, the reversed drive is only exceptionally used when e.g. a joint is unfastened. This implies that the main focus of the motor and the transmission is on the forward drive.
A problem that needs to be addressed in a hand held power wrench is that the torque provided by the tool needs to be compensated for, such that a counter force is provided for every torque provided by the tool. In a pulsating power wrench most of these counter forces are compensated for by the functional design of the tool itself. This may also be the case in sophisticated continuously driven or non-pulsating tools. In other tools, the counter forces have to be provided by the operator who is holding the tool.
Often, the rotational speed of the motor may be adapted to smoothen or level out the torque provided in the forward direction. This is possible because the torque is relatively low in a first stage, such that inertia is build up to balance out part of the torque as it increases towards the end of the operation. In the reversed direction the conditions are however normally different, because the reversed direction is normally utilised to loosen a joint, which is fastened by a relatively high clamp force, which may only be released by a correspondingly high torque. Hence, often, a high torque needs to be delivered right away, such that it is not possible to build up inertia in the machine.
Therefore, there is a need of a tool that functions well in the forward direction, but that may be adapted or tuned so as to function better than a conventional power wrench in the reversed direction.